made apply non-blocking by using a meta-task

docs/source/pages/pool.rst

@@ -228,8 +228,6 @@ The only method of a pool that one should **always** assume to be blocking is :p
 
 One method to be aware of is :py:meth:`.flush() <asyncio_taskpool.pool.BaseTaskPool.flush>`. Since it will await only those tasks that the pool considers **ended** or **cancelled**, the blocking can only come from any callbacks that were provided for either of those situations.
 
-In general, the act of adding tasks to a pool is non-blocking, no matter which particular methods are used. The only notable exception is when a limit on the pool size has been set and there is "not enough room" to add a task. In this case, both :py:meth:`SimpleTaskPool.start() <asyncio_taskpool.pool.SimpleTaskPool.start>` and :py:meth:`TaskPool.apply() <asyncio_taskpool.pool.TaskPool.apply>` will block until the desired number of new tasks found room in the pool (either because other tasks have ended or because the pool size was increased).
+In general, the act of adding tasks to a pool is non-blocking, no matter which particular methods are used. The only notable exception is when a limit on the pool size has been set and there is "not enough room" to add a task. In this case, :py:meth:`SimpleTaskPool.start() <asyncio_taskpool.pool.SimpleTaskPool.start>` will block until the desired number of new tasks found room in the pool (either because other tasks have ended or because the pool size was increased).
-
-:py:meth:`TaskPool.map() <asyncio_taskpool.pool.TaskPool.map>` (and its variants) will **never** block. Since it makes use of a "meta-task" under the hood, it will always return immediately. However, if the pool was full when it was called, there is **no guarantee** that even a single task has started, when the method returns.
-:py:meth:`TaskPool.map() <asyncio_taskpool.pool.TaskPool.map>` (and its variants) will **never** block. Since it makes use of a "meta-task" under the hood, it will always return immediately. However, if the pool was full when it was called, there is **no guarantee** that even a single task has started, when the method returns.
 
+:py:meth:`TaskPool.apply() <asyncio_taskpool.pool.TaskPool.apply>` and :py:meth:`TaskPool.map() <asyncio_taskpool.pool.TaskPool.map>` (and its variants) will **never** block. Since they make use of "meta-tasks" under the hood, they will always return immediately. However, if the pool was full when one of them was called, there is **no guarantee** that even a single task has started, when the method returns.

src/asyncio_taskpool/pool.py

@@ -668,7 +668,9 @@ class TaskPool(BaseTaskPool):
 
         All the new tasks are added to the same task group.
 
-        This method blocks, **only if** the pool has not enough room to accommodate `num` new tasks.
+        Because this method delegates the spawning of the tasks to a meta task, it **never blocks**. However, just
+        because this method returns immediately, this does not mean that any task was started or that any number of
+        tasks will start soon, as this is solely determined by the :attr:`BaseTaskPool.pool_size` and `num`.
 
         Args:
             func:
@@ -701,8 +703,9 @@ class TaskPool(BaseTaskPool):
             group_name = self._generate_group_name('apply', func)
         group_reg = self._task_groups.setdefault(group_name, TaskGroupRegister())
         async with group_reg:
-            task = create_task(self._apply_num(group_name, func, args, kwargs, num, end_callback, cancel_callback))
+            meta_tasks = self._group_meta_tasks_running.setdefault(group_name, set())
-        await task
+            meta_tasks.add(create_task(self._apply_num(group_name, func, args, kwargs, num,
+                                                       end_callback=end_callback, cancel_callback=cancel_callback)))
         return group_name
 
     @staticmethod

tests/test_pool.py

@@ -513,8 +513,7 @@ class TaskPoolTestCase(CommonTestCase):
         mock__generate_group_name.return_value = generated_name = 'name 123'
         mock_group_reg = set_up_mock_group_register(mock_reg_cls)
         mock__apply_num.return_value = mock_apply_coroutine = object()
-        mock_task_future = AsyncMock()
+        mock_create_task.return_value = fake_task = object()
-        mock_create_task.return_value = mock_task_future()
         mock_func, num, group_name = MagicMock(), 3, FOO + BAR
         args, kwargs = (FOO, BAR), {'a': 1, 'b': 2}
         end_cb, cancel_cb = MagicMock(), MagicMock()
@@ -525,10 +524,11 @@ class TaskPoolTestCase(CommonTestCase):
             mock__check_start.assert_called_once_with(function=mock_func)
             self.assertEqual(mock_group_reg, self.task_pool._task_groups[_group_name])
             mock_group_reg.__aenter__.assert_awaited_once_with()
-            mock__apply_num.assert_called_once_with(_group_name, mock_func, args, kwargs, num, end_cb, cancel_cb)
+            mock__apply_num.assert_called_once_with(_group_name, mock_func, args, kwargs, num,
+                                                    end_callback=end_cb, cancel_callback=cancel_cb)
             mock_create_task.assert_called_once_with(mock_apply_coroutine)
             mock_group_reg.__aexit__.assert_awaited_once()
-            mock_task_future.assert_awaited_once_with()
+            self.assertSetEqual({fake_task}, self.task_pool._group_meta_tasks_running[group_name])
 
         output = await self.task_pool.apply(mock_func, args, kwargs, num, group_name, end_cb, cancel_cb)
         check_assertions(group_name, output)
@@ -540,8 +540,6 @@ class TaskPoolTestCase(CommonTestCase):
         mock__apply_num.reset_mock()
         mock_create_task.reset_mock()
         mock_group_reg.__aexit__.reset_mock()
-        mock_task_future = AsyncMock()
-        mock_create_task.return_value = mock_task_future()
 
         output = await self.task_pool.apply(mock_func, args, kwargs, num, None, end_cb, cancel_cb)
         check_assertions(generated_name, output)